Method of making electric cables



July 31, 1962 R. 5. FELLER ETAL 3,047,448

METHOD OF MAKING ELECTRIC CABLES Filed June 7, 195'? United States This invention relates to an improvement in electric cables.

One object of our invention is to provide an electric cable capable of continuous operation at temperatures up to 200 C.

Another object of the invention is to provide an electric cable capable of continuous operation at temperatures up to 200 C. in which corona discharge between the cable conductor and its insulation is reduced to a minimum.

More specifically, our improved cable essentially comprises a conductor insulated with a cured silicone-base insulating compound. Intermediate the cable insulation and the cable conductor we provide a cured semi-conducting silicone layer.

In fabricating some types of cablefor example, a pulse cablein accordance with our invention, we en-' close' the insulating wall in an adherent semi-conducting silicone layer. 7

In curing the semi-conducting silicone layer or layers as well as the insulating silicone wall, similar curing agents are employed. We also employ similar silicone polymers atent or gums for the insulating wall and the semi-conducting layer or layers.

The inner semi-conducting layer, viz., the layer immediately surrounding the cable conductor, may be ap' plied to the conductor in the form of a tape, or it may be extruded directly upon the conductor, but in either case it must be partially cured before the application of the insulating wall. Where the semi-conducting layer is applied to the conductor as a tape, it must be partially cured not only before the application ofthe insulating Wall but before the tape is applied to the conductor. If, on the other hand, the semi-conducting layer is extruded directly about the conductor, it must be partially cured after extrusion and before the application of the insulating wall.

When employing tape as the inner layer, completion of thecuring of this layer andthe entire cure of the insulating wall is effected in situ. Where the inner layer is extruded upon the conductor, it will be appreciated that the completion of curing is done in situ.

As above pointed out, in some types of cablessuch as a pulse cable, for example-we not only employ a semi-conducting layer beneath the insulation, but we apply a semi-conducting, silicone adherent layer upon the exterior of the insulating wall as well. In such a cable the procedure is the sameas already described, so far as application of the inner layer and of the insulating Wall is concerned, but we only partially cure the inner 3,647,448 Patented July 31, 1962 ice vsitu.

Semi-conducting mixtures employing various types of silicones as a base essentially contain large amounts of conductingblack, the presence of which inhibits curing of these mixtures by peroxide curing systems normally used in the curing of silicone insulating compounds. Accordingly, an attempt was made to produce a cable employing a sulfur-curing, semiconducting silicone mixture for the semi-conducting layer. We were able to cure such a material satisfactorily, but we found that the presence of such material, after uncured or precured, adjacent an insulating wall of normal peroxide-curing silicone resulted in complete inhibition of cure of the insulating wall.

Also an attempt was madeto produce a cable employing a di-tertiary butyl peroxide-curing, semi-conducting compound based on silicone gum having a low mole percentage of vinyl methyl siloxane groups. This semiconducting compound cured very .well, but, when placed either in the cured or uncured state adjacent an insulating Wall of benzoyl peroxide-curing silicone, the result was severe inhibition of cure of the insulating wall.

We have discovered, however, that we are able suc cessfully to produce a cable having satisfactory physical, electrical, and aging characteristics by employing a guru having a low mole percentage of vinyl methyl siloxane groups, such as a silicone gum known commercially as W-96 and manufactured by the Silicone Division of Union Carbide and Carbon Corporation, as the base for the semi-conducting material and for the insulating compound, and bycuring both the semi-conducting material and the insulating compound with di-tertiary butyl amounts of vinyl alkylsiloxanes in which the range of vinyl concentration is between a 1:350 and 1:340 vinyl to silicon ratio. These gums will be referred to hereinafter as vinyl-containing silicone gums.

For achieving maximum conductivity, so far as the semi-conducting material is concerned, we have found a conducting black, such as acetylene black, for example, the most effective.

In the accompanying drawings,

FIG. 1 shows in elevation a cable embodying our invention; and

FIG; 2 is a similar view showing another embodiment of the invention. i

Referring to FIG. 1 of the drawings, 2 designates the cable conductor. Immediately about this conductor is a semi-conducting adherent layer 4. This layer is enclosed in an adherent insulating wall 6. 8 designates a metal shield or outer conductor. 7

The cableis sheathed or jacketed in a sheath or jacket 19 of anyof the materials conventionally employed for this purpose in the electric cable industry.

The semi-conducting layer 4 is made from a mixture comprising the following ingredients:

Parts by weight Vinyl-containing silicone gum 100 Conducting Black 4070 Di-tertiary butyl peroxide or di-cumyl peroxide" 4-8 It will be appreciated that the amount of conducting enemas black employed depends upon the desired conductivity in the finished product, hence, the range of from forty to seventy parts by weight above set out. In practice, compounds having volume-resistivities lower than 1 ohmczn. have been obtained and used in manufacture.

In practice, the above compound may be calendered to a selected width and thickness, partially cured by exposure in air for one minute at 450 F, and then wrapped as a tape about the cable conductor 2 to provide an adherent semi-conducting layer.

The insulating wall 6 is made from a mixture comprising the following ingredients: V Parts by weight Vinyl-containing silicon gum 100 Silica 30l20 Dl-tertiary butyl peroxide or di-cumyl peroxide 13 The amount of silica. used will depend mainly on the physical and electrical properties desired and on the type of silica employed.

The above mixture may be extruded about the semiconducting layer 4. The assembly is then subjected to a curing action, completely to cure the insulation and to complete the curing of the semi-conducting layer in situ.

, The semi-conducting compound composing the layer 4 may be extruded directly about the conductor 2 and then subjected to the action of air for one minute at 450 F. The insulating compound composing the wall 6 is then extruded about the layer 4, after which the insulating compound is cured and curing of the layer 4 completed in situ.

As previously noted, in some types of electric cable it is necessary to provide a semiconducting layer over the insulating wall. We have shown such a cable in FIG. 2.

Referring to this view, 12 designates the cable conductor. To this conductor We apply a semiconducting layer 14, the ingredients of which are the same as those of the semi-conducting layer 4 of FIG. 1. This com- 7 pound may be extruded directly upon the conductor, after which it is partially cured by exposure in air for one minute at 450 F. Immediately about the semi-conducting layer :14 we extrude an insulating wall 16. The ingredients of this Wall are the same as those of the insulating Wall 6 of FIG. 1, and after this Wall has been applied, we effect a further cure of the semi-conducting layer and a partial cure of the insulating Wall 16.-

Over the partially cured insulating Wall 16 we extrude a semi-conducting layer 18, the ingredients of which are the same as those of semi-conducting layer 14. The assembly is then subjected to a curing action, completely to cure the outer semi-conducting layer 18 and to complete the cure of the underlying insulating wall 16 and the inner semi-conducting layer 14.

'19 designates a metal shield or outer conductor, corresponding to the shield or outer conductor 8 of FIG. 1, and 20 designates the outer jacket or sheath.

The outer semi-conducting layer 18 may be applied in partially cured tape form to the partially cured insulating wall -16. In that event, the mixture which is to compose the layer 18 is calendered to a selected width and thickness and then partially cured by exposure in air at a temperature of around 450 F. It is then wrapped around the insulating wall 16 and the assembly subjected to a curing action to complete the curing of the two semi-conducting layers 1.4 and 18 and of the insulating wall 16 in situ.

This application is a continuation-in-part of our copending application Serial No. 592,950, filed June 21, 1956.

What we claim is:

1. The method of manufacturing an electric cable capable of continuous operation at temperatures up to 200 C., which method comprises applying to the cable conductor an incompletely cured, semiconducting tape capable of continuous operation at temperatures up to 200 C., which method comprises applying to the cable conductor an incompletely cured, semi-conducting tape consisting of a vinyl-containing silicone gum, conducting black, and a curing agent selected from the group consisting of di-tertiary butyl peroxide anddi-cumyl peroxide; applying an uncured insulating layer about said partially cured tape, said insulating layer consisting of a vinyl-containing silicone gum, silica, and a curing agent selected from the group consisting of di-tertiary butyl peroxide and di-curnyl peroxide; subjecting the assembly to a curing operation to efiect further but incomplete curing of the semi-conducting tape and partially to curethe in,- sulating layer; applying a semi-conducting, partially cured tape consisting of a vinyl-containing silicone gum, conducting black, and a curing agent selected from the group consisting of di tertiary butyl peroxide and di-cumyl peroxide about the insulating layer; and subjecting the assembly to a curing operation to effect completion of the curing of the first-mentioned, partially cured tape, the partially cured insulating layer, and the last-mentioned, partially cured semi-conducting tape in situ.

3. The method of manufacturing an electric cable capable of continuous operation at temperatures up to 200 C., which method comprises extruding an uncured semi-conducting layer about the cable conductor, said layer consisting of a vinyl-containing silicone gum, conducting black, and a curing agent selected from the group consisting of iii-tertiary butyl peroxide and di-cumyl peroxide; effecting partial curing of the said layer in situ; extruding an uncured insulating layer about said partially curved semi-conducting layer, said insulating layer consisting of a vinyl-containing silicone gum, silica, and a curing agent selected from the group consisting of ditertiary butyl peroxide and di-cumy1 peroxide; and efiecting completion of the curing of the partially cured semiconducting layer and the complete curing of the uncured insulating layer in situ.

4. The method of manufacturing an electric cable capable of continuous operation at temperatures up to 200 C., which method comprises extruding an uncured semi-conducting layer about the cable conductor, said layer consisting of a vinyl-containing silicone gum, conducting black, and a curing-agent selected from the group consisting of di-tertiary butyl peroxide and di-cumyl peroxide; etfecting partial cun'ng of the said layer in situ; extruding an uncured insulating layer about said partially cured semi-conducting layer, said insulating layer consisting of a vinyl-containing silicone gum, silica, and a curing agent selected from the group consisting of ditertiary butyl peroxide and di-cumyl peroxide; effecting further curing of the partially cured semi-conducting layer and partial curing of the uncured insulating layer; extruding an uncured semiconducting layer about said partially cured insulating layer, said lastmentioned semi-conducting layer consisting of a vinyl-containing silicone gum, conducting black, and a curing agent selected from the group consisting of di-tertiary butyl peroxide and dicumyl peroxide; and effecting completion of the curing of the first-mentioned semi-conducting layer and of the insulating layer and complete curing of the last-mentioned semi-conducting layer in situ.

(References on following page) UNITED STATES PATENTS Bormann Oct. 21, 1941 Boggs May 21, 1932 Bower Aug. 17, 1937 Scott et a1 Dec. 8, 1942 6 Frisco Sept. 9, 1947 Gillis Aug. 23, 1949 Marsden Sept. 5, 1950 Weyenberg July 26, 1955 Marshall et a1 Apr. 16, 1957 Dickmann Aug. 20, 1957 

1. THE METHOD OF MANUFACTURING AN ELECTRIC CABLE CAPABLE TO CONTINUOUS OPERATION AT TEMPERATURES UP TO 200*C., WHICH METHOD COMPRISES APPLYING TO THE CABLE CONDUCTOR AN INCOMPLETELY CURED SEMI-CONDUCTING TAPE CONSISTING OF A VINYL-CONTAINING SILICONE GUM, CONDUCTING BLACK, AND A CURING AGENT SELECTED FROM THE GROUP CONSISTING OF DI-TERTIARY BUTYL PEROXIDE AND DI-CUMYL PEROXIDE; APPLYING AN UNCURED INSULATING LAYER ABOUT SAID PARTIALLY 